In recent years, non-thermal plasma generated in a packed bed reactor has been shown to be effective in reducing nitric oxides (NOx) produced by power plants and standby generators. These units usually have a reducing agent, such as urea, to enhance the conversion efficiency. The packed bed reactor consists essentially of a high voltage center electrode inserted into a cylinder of dielectric material, usually a form of glass or quartz.
An outside or ground electrode is formed by a coating of metal in various forms, including tape, flame spray, mesh, etc. The space between the center electrode and the inside diameter of the dielectric tube is filled or packed with small diameter glass beads. When high voltage alternating current is applied to the center electrode, the surfaces of the beads go into corona, producing a highly reactive and selective surface for inducing the desired reaction in the gas.
Unfortunately, the packed bed design with its loose beads and glass dielectric is impractical for use in the conditions found in a mobile emitter, such as a car or truck. The vibration and wide temperature swings of the vehicle system would damage the packed bed and the necessary temperature and vibration isolation needed to make it survive would not be cost effective.
A stacked plate reactor for use with diesel engines and other engines operating with lean air fuel mixtures is disclosed in commonly assigned U.S. patent application Ser. No. 09/465,073 entitled “Non-thermal Plasma Exhaust NOx Reactor,” which is hereby incorporated by reference herein in its entirety. Disclosed therein is a reactor element comprising high dielectric, nonporous, high temperature insulating means defining a group of relatively thin stacked cells forming gas passages and separated by the insulating means. Alternate ground and charge carrying electrodes in the insulating means on opposite sides of the cells are disposed close to, but electrically insulated from, the cells by the insulating means. The electrodes may be silver or platinum material coated onto alumina plates. Conductive ink is sandwiched between two thin nonporous alumina plates or other suitable insulating plates to prevent arcing while providing a stable electrode spacing for a uniform electric field. The electrodes are coated onto alumina in a pattern that establishes a separation between the electrodes and the connectors of alternate electrodes suitable to prevent voltage leakage.
In commonly assigned U.S. Provisional Application Ser. No. 60/141,427 filed Jun. 29, 1999 entitled “Design and Method of Manufacturing a Plasma Reactor for Treating Auto Emissions —Stacked Shapes,” which is also hereby incorporated by reference herein in its entirety, a non-thermal plasma reactor element is prepared from formed building blocks of dielectric material. The formed shape defines an internal cell in the plasma reactor having an exhaust passage for flowing exhaust gas to be treated therethrough. Individual cells are provided with a conductive print disposed thereon to form electrodes and connectors. In a preferred embodiment, the conductive print comprises a continuous grid pattern having a cutout region disposed opposite the terminal connector for reducing potential voltage leaks. Multiple cells are stacked and connected together to form a multi-cell stack.
Commonly assigned U.S. Provisional Application Ser. No. 60/141,401 filed Jun. 29, 1999 entitled “Method of Manufacturing A Plasma Reactor For Treating Emissions —Durable and Low Cost,” which is hereby incorporated by reference herein in its entirety, and commonly assigned U.S. Provisional Application Ser. No. 60/141,403 filed Jun. 29, 1999 entitled “Design and Method Of Manufacture Of a Plasma Reactor With Curved Shape For Treating Auto Emissions,” which is also incorporated by reference herein in its entirety, disclose a reactor and method for preparing same, respectively. The reactor is characterized by a reactor element prepared from a curved, swept-shaped substrate specifically designed for fabrication via extrusion. The as-extruded curved substrate comprises a thick outer wall surrounding a plurality of channels separated by dielectric barriers. Selected channels are coated with a conductive material to form conductor channels. The prepared reactor element comprises multiple concentric exhaust channels, multiple concentric conductor channels having alternating polarity, each connected to its respective polarity via bus paths, in-line structural support ligaments for providing optimal structural support while preventing exhaust leakage, and thick outer walls providing high crush resistance and allowing robust mounting into the reactor housing.
While the above non-thermal plasma reactors meet some of the current needs and objectives, there remains a need in the art for an improved, durable, low cost non-thermal plasma reactor and improved method of manufacturing same. There further remains a need for a non-thermal plasma reactor that can be prepared with reduced manufacturing complexity, reduced number of components and reduced overall material cost.